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Wiring a new home workshop

01-30-2014, 09:23 PM

I am not an electrician but I do have a little bit of experience in house wireing and a lot more experience wiring boats and automobiles. What I wanted to do here is just toss out some thoughts for guys who want to run dedicated circuits into their home shops safely.

You know why the line to your shiny new welder has a fuse (circuit breaker) in it? It is not there to protect your welder or any other terminal device. Nope, that ain't it. The breaker is there for one purpose and one only. Its there to protect the wire - which in likelyhood is inside a wall where it can't be seen or monitored for heat build up.

If your house is somewhat new it likely that you have a breaker panel (fuse box) that is rated at 200 amps. Right at its top it will have a main breaker of that capacity. The actual service to your home may very well be higher powered than that, ours for instance has 360 amp service going in. My point is that the entrance defines how much you have to work with in total.

When you decide to wire an outlet for your home-shop welder it is important that you know how much power it will consume at its highest use and the build in over protection from the breaker all the way to the welder's plug. You can never be too safe when it comes to the potential for home fires.

So, you start by determining what your maximum load will be and then you build to accommodate it. I'll give a real-life example in a moment. By build to accommodate I mean to size your breaker, wires, and outlet to the task at hand. The bigger the wire the more power it can carry safely. How big? Well, its a matter of amperes (amps). More amps demand heavier wire. Here are some simple guidelines:

14 ga. wire is good for up to 15 amps
12 ga. wire is good for up to 20 amps
10 ga. wire is good for up to 30 amps
6 ga. wire is required for up to 50 amps. (edited to change wire size)

Now, a 'how I did it" for wiring the dedicated outlet for a small welder. The welder I bought last week (MM211) draws just under 30 amps at maximum load. It draws so close to 30 amps that a 30 amp circuit was out of the question, we built in our first level of protection by installing a 40 amp breaker, about 35% over the minimum need and not one single dime more expensive than a 30 amp breaker. We then wired it with 8 gauge wire, which for our 50-foot run from the breaker box to the outlet cost me about $25 more than the next size down. Cheap insurance that will last a lifetime. The outlet (NEMA 6-50 if I remember correctly) is already sized for its power requirement so it is what it is. Wiring of the circuit was straight forward except that the outlet is peculiar in that no neutral wire is used; just two hots and a ground. I won't go into "bonding" but somewhere back in my "Service Entry" there is a little green screw that connects the existing neutral wire to the ground plane (earth) and that allows it to work and also conform to the National Electric Code (NEC).

What that means is that my welder, which draws 28.something amps is fed first by an outlet that is rated for 50 amps, which is fed by wires that are entirely capable of providing the 40 amps of power my 40-amp circuit breaker will allow to pass with no fear of fire.

And that's the story, size up, don't take a chance, it too cheap to do it safely and its a lifetime investment in your own safety.

And then there is the matter of extension cords. I would no more use a 14 or 12 ga. extension cord to power my welder than I would hit a honet's nest with a hammer. For one thing the heat that will build up in that wire is heat that is not available for welding - its just wasted. Heavy cords not only reduce wasted energy but they also prolong the life of the device they power, a somewhat expensive blue box in this case.

And that's my story. Do not skimp when installing your power, it is false economy at best and can not only lead to home fires but also can eat into the life expectancy of your equipment. An extra $50 spend now can save you a lot more than headaches down the road.

Last edited by 1_old_man; 02-01-2014, 06:58 PM.
Reason: Edited in response to member comments, my bad.

Nice report but I'll dissagree on wire size for the 50 amp line the recomended wire size is #6 not #8.
I made a 100 foot extension for my welders the lincoln needs 50 amp if run full power the #6 wire is good for a max of 55 amps, works well no proublem's.

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So since the discussion is on home/shop electric I have a question. I'm about to put a 200A service in my shop. I have to run 70' from meter base/service pole to panel, what size wire do I need? I have wire from a temporary service pole (not sure of size) I'm hoping to use. There are no markings on wire coating either, how can you tell what size it is? Its aluminum.

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What is your location ? Single or three phase ? Did you pull a permit ? Many towns have electrical building department where all work is inspected. They may even have their own electrical code book which will answer your questions. Some areas will not allow aluminum for main service. You need to check local requirements. One may allow 2/0 while another is 3/0. I would not use aluminium only copper.

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As I said, I am no electrician. I limit my knowledge to knowing that somewhere there is either a requirement and if not that then there is an industry standard. I live in an area with no building codes what so ever. No inspections, no nothing other than the County will have to be in on your septic system. But as for structural or electrical - you can build anything you want. Now how yourinsurance agent feels about that may be a much different matter, it is his demands and the minimum requirement of the National Code that drive everything we (my son and I are building and wiring a house for him and his) have been following. So while I can't give any advice as to an answer to your question I can tell you that it will be found either in local codes or at the national level.

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Im in Kentucky, system will not need to be inspected because I'm adding to the system from a main breaker off of meter base pole. The system from pole to meter and meter to house is all aluminum now. I already have a section of aluminum is only reason I was going to use it, I know copper is better, but trying use what I already have what was given to me... Is there anyway of telling the size of wire I have if no markings on the coating?

You should follow all local codes and the National Electrical Code. You don't want to go cheap. No inspection ? After a fire the insurance investigator will tell you if you followed code or not. Sad way to find out that insurance carrier will not cover damage or loss. Had similar situation where a buddy installed a old HOUSE furnace in garage. Fire started with furnace issues. Insurance carrier declined coverage because furnace was not approved for garage installation. I know, many do it and are lucky.

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I love how people say , we don't have building code. Even square inch of United States has building code, some are just not enforced due to budget. Like one guy said, let something happen and watch what the lawyers do to you.

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I love how people say , we don't have building code. Even square inch of United States has building code, some are just not enforced due to budget. Like one guy said, let something happen and watch what the lawyers do to you.

No code what so ever exists in most West Virginia counties. It's not that there is a code but laxed enforcement. There is simply no code to be enforced,no ale or ordinance requiring standards must be met,no office of inspectors, in fact no inspectors at all. No inspections' no certificates of occupancy, and not a soul to call if you just want to do it right and could use assistance, and if we tried to get any of that good stuff listed avove it would be voted down faster than the ballot could be counted. You would be suprised how strongly people will cling to a very bad system.

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While reading this discussion it occurred to me that when replacing the power cord plug on my MillerMatic 130 after a car parked on it a few months ago, I just simply replaced the plug without paying any attention to polarity of the wires.
I do not use this welder often and it seems to have been acting difficult the last few times I welded with it.
Question is: does it matter which wire goes to which plug blade and if so , how do I determine which wire goes where.
I hope this is not too far off topic but as this is somewhat related I do not want to start a new thread.
Any advice would be appreciated.